Vladimir A. Pomogaev

Luminescence Solvato- and Vapochromism of Alkynyl-Phosphine Copper Clusters

The reaction of [Cu(NCMe)4][PF6] with aromatic acetylenes HC2R and triphosphine 1,1,1-tris(diphenylphosphino)methane in the presence of NEt3 results in the formation of hexanuclear Cu(I) clusters with the general formula [Cu6(C2R)4{(PPh2)3CH}2][PF6]2 (R = 4-X-C6H4 (1-5) and C5H4N (6); X = NMe2 (1), OMe (2), H (3), Ph (4), CF3 (5)). The structural motif of the complexes studied consists of a Cu6 metal core supported by two phosphine ligands and stabilized by σ- and π-coordination of the alkynyl fragments (together with coordination of pyridine nitrogen atoms in cluster 6). The solid state structures of complexes 2-6 were determined by single crystal XRD analysis. The structures of the complexes in solution were elucidated by (1)H, (31)P, (1)H-(1)H COSY NMR spectroscopy, and ESI mass spectrometry. Clusters 1-6 exhibit moderately strong phosphorescence in the solid state with quantum yields up to 17%. Complexes 1-5 were found to form solvates (acetone, acetonitrile) in the solid state. The coordination of loosely bound solvent molecules strongly affects emission characteristics and leads to solvato- and vapochromic behavior of the clusters. Thus, solvent-free and acetonitrile solvated forms of 3 demonstrate contrasting emission in orange (615 nm) and blue (475 nm) regions, respectively. The computational studies show that alkynyl-centered IL transitions mixed with those of MLCT between the Cu6 metal core and the ligand environment play a dominant role in the formation of excited states and can be considerably modulated by weakly coordinating solvent molecules leading to luminescence vapochromism.

Absorption Spectra of Estradiol and Tryptophan Constructed by the Statistical and Elongation Methods

The statistical quantum chemical/molecular dynamical method is developed and employed to reproduce optical spectra. This technique includes quantum-mechanical calculations on energy states and photophysical properties of molecular conformers obtained during molecular dynamical simulation. Polycyclic organic molecule estradiol surrounded by solvent particles and protein structure including tryptophan fragment under thermodynamical conditions are considered. A wide absorption spectrum over several excited electronic states of estradiol is constructed. First longwave absorption band of tryptophan-cage mini protein is built involving the elongation method. These statistical spectra reflect the main features of the corresponding experimental ones.

Three-center integrals of one-electron operator of a spin-orbit interaction

A computational algorithm for three-center integrals in matrix elements of a spin-orbit interaction operator is developed. The explicit form of the integrals is derived. Empirical and calculated atomic constants of the spin-orbit interaction are compared. The effect of interatomic spacing in the atom chain on the magnitude of integrals is considered. Distinctions between one-center and multicenter approximations as well as the range of application are analyzed using planar and nonplanar compounds as examples.

SPIN-ORBITAL INTERACTION IN MOLECULAR COMPLEXES OF NAPHTHALENE WITH ANTHRACENE DERIVATIVES

A new computational procedure for the rate constant of intercombination conversion is developed within the framework of standard quantum chemical calculations. The differences and limits of applicability of concentric, π, and multicenter approximations are analyzed. The possibility of energy transfer in complexes of anthracene derivatives and naphthalene is considered.

Optical properties of two types of sex hormones of the cyclopentenephenanthrene series

The spectral and luminescent characteristics of estradiol and testosterone—two basic sex hormones of the cyclopentenephenanthrene series—are calculated by employing quantum-chemical methods. The results of calculations are in good agreement with experimental data. It is shown that fluorescence observed in estrogens is associated with the occurrence of the lowest ππ state, while the absence of fluorescence in androgens is attributed to the existence of the lowest nπ state, from which fluorescence is forbidden.

T S Energy Transfer in Some Molecular Complexes

Calculations on the bimolecular complexes of acetophenone or benzophenone with anthracene and its substituted derivatives were carried out using a standard quantum-chemical approach to molecular systems. The deactivation pathways for lower triplet excited states of acetophenone and benzophenone were established. The probability of energy transfer from the energy donor to acceptor in the complexes was considered. The analysis of calculation results showed that the T → S transfer of electronic excitation energy in these complexes is feasible only in the case of a small distance between the molecules, and the efficiency of this transfer is higher in the acetophenone rather than benzophenone complexes.

Atomic structure and physical properties of fused porphyrin nanoclusters

The atomic and electronic structures, mechanical properties and potential barriers of formation of a set of meso–meso β–β fused porphyrin/metalloporphyrin nanopages, nanotapes, nanotubes and 2D nanofabrics were studied by GGA LC-DFT technique using cluster and PBC models. The porphyrin pages of the nanoclusters are connected with each other by graphene fragments formed by meso–meso β–β links. Fusion of all the edges of six porphyrin/metalloporphyrin units produces a novel ~ 1 nm sized molecule of cubic symmetry with a hollow cage inside. It was found that all studied nanoclusters are metastable with formation energies 0.36–7.57 kcal/mol per atom. Under applied mechanical stress, the nanoclusters exhibit superelastic and ultrastrong properties with binding graphene fragments being the weakest links for mechanical rupture. Depending on the spin-dependent reaction pathways, the hollow caged nanoclusters exhibit almost zero or low potential energy barriers (1–10 kcal/mol) during the initial stages of self-assembly. All nanoclusters exibit the main features of the electronic structures of the parent porphyrins, in particular the nature of HOMO/LUMO states and the relative energetic positions of the metal d states. The induced curvature of the hollow cage nanoclusters leads to admixture of more than 2% of the dπ⊥ states to the dσ energy region and formation of vacant superatomic molecular orbitals of d character in cubic ligand field. The Fe-derived hollow-caged nanoclusters reveal extremely high spin states with small energy differences between ferromagnetic and antiferromagnetic configurations, which can be utilized for quantum holonomic computations.

Inheritance of Photochromic Properties of Nitro-Substituted and Halogenated Spiropyrans Containing the Pyrrolidino[60]fullerene

The photophysical and isomerization properties of hybrid molecular compounds that consist of photochromic nitro-substituted and halogenated spiropyran derivatives bonded to the surface of the [60]fullerene cage through the pyrrolidine bridge were investigated using various functionals and basis sets of TD-DFT and semiempirical quantum-chemical approaches. The role of nπ* states formed by the lone pairs of substituents in changing of the electronic structure and photochromic properties of spiropyran derivatives was evaluated. The Sππ(spiropyran) → intermediate nπ* states → Sππ(merocyanine) channel for phototransformation of the hybrid compound containing a nitro-substituted spiropyran moiety was established and compared with similar systems of halogenated spiropyrans attached to the [60]fullerene bulk where photoinduced isomerization does not process due to high probability of internal conversion from the excited electronic state localized on the spiropyran fragment to the states of the pyrrolidino[60]fullerene.

INVESTIGATION OF THE HEAVY-ATOM EFFECT ON THE SPECTRAL-LUMINESCENT PROPERTIES OF DICHLOROANILINES

The influence of the chlorine atom position on the spectral, geometric, and photophysical characteristics of free molecules of dichloroaniline is studied by electron spectroscopy, fluorescence, and quantum chemistry. A chlorine atom included in the aniline aromatic ring is shown to exhibit properties inherent in a heavy atom, that is, the radiation is dominated by phosphorescence. According to quantum-chemical calculations, the quenching of fluorescence is due to the fact that the efficiency of the intersystem crossing conversion proves to be much higher than the radiative decay rate of the S1 state.

Effect of substituents and protonation on photolysis of the 2,5-diphenyl-oxazole molecule

Based on quantum chemical calculations, we consider the effect of substitution by groups with different donor-acceptor properties and protonation on the probability of opening of the oxazole ring of the 2,5-diphenyloxazole molecule (PPO). We show the determining role of the hydrogen-containing medium in this photoconversion. We have established that a substituent introduced into the para position of the 5-phenyl radical, depending on its donor-acceptor properties, can either enhance the efficiency of photolysis (donor substituent) or weaken it (acceptor substituent). We have found the photodissociative states and have determined their multiplicity for the considered substituted PPOs.